1. Field of the Invention
This invention relates to a shearing device for use in shearing a sheet material such as a metal sheet or plate, paper or cloth, wherein a material for a shearing device such as cemented carbide or high-hardness hardened steel is rigidly anchored in the tool body. To maintain constant the clearance between an upper and lower shearing edge members along the lengths thereof, the shearing edge member of the respective shearing tool should be finished straight at high precision, from the view points of the desired functions of a shearing device.
2. Description of the Prior Art
A shearing device of the type of the prior art has been such that, as shown in FIG. 1, a material for shearing edge member 12 is soldered to a tool body 11 with a hard solder. The soldering with a hard solder suffers from a drawback that, when soldering, heat at more than 500.degree. C. is applied to the tool body 11 and shearing edge member 12, so that there results a strain in the shearing device thus prepared due to the difference in coefficient of thermal expansion and phase transformation between the material of the tool body 11 and the material of the shearing edge member 12, or there result adhesion of scales to the shearing device. To remove a strain from the shearing device to provide a highly precise and straight tool, many man hours are required for a machining process.
In case a piece of S45C of 10 mm.times.40 mm (JIS carbon steel for construction) is used as a tool body, a piece of SKH 9 of 3 mm.times.15 mm (JIS high speed tool steel) is used as a material for shearing edge member, and both are joined with silver brazing alloy of a melting point of 700.degree. C., then there is produced a shearing device with a curvature S of 0.2 to 0.5 mm or thereabout per 100 mm in length, as shown in FIG. 2.
In case cemented alloy is used as a material for the shearing edge member, the difference in coefficient of thermal expansion between the cemented alloy and the material of the tool body becomes more evident, so that a curvature of the device, resulting from the soldering of these materials, becomes greater. In case tungsten carbide (WC) is used as a material for a shearing edge member which is hard-soldered to the tool body under the same condition as in the above case, a resultant curvature of 1 to 1.5 mm per 100 mm in length results. This is due to the fact that the coefficient of thermal expansion of steel is 10-12.times.10.sup.-6 /.degree.C. and in contrast thereto, that of tungsten carbide is 5-8.times.10.sup.-6 /.degree.C. which is half the value of steel. It is a requisite for a shearing device that a curvature in the device be normally maintained below 0.01 mm. For this reason, a shearing device having a curvature of more than that value need be repeatedly subjected to the finishing process, in which a straightening process by means of a press or hammer and a grinding process are carried out alternately, so that a straight shearing device may be provided. Such a finishing process generally entails many steps, particularly the straightening process requiring an extreme skill.
In case soft solder is used for joining the shearing edge member 12 to the tool body 11, strain as well as scales is greatly reduced in amounts, because of the use of relatively low heating temperature, as compared with those used in the hard soldering. However, the joints produced by soft soldering suffer from a drawback that the tool body 11 and the shearing edge member 12 are apt to be separated from each other during its service. Such a shearing device is not adapted for actual use, unless the construction of a shearing device is modified.
The silver solder (hard solder) whose melting point is about 700.degree. C. presents a tensile strength of 40 to 60 Kg/mm.sup.2, while soft solder whose melting point is about 300.degree. C. presents a tensile strength of 5 to 15 Kg/mm.sup.2, which is too low to satisfy a required strength.
It is accordingly an object of the present invention to provide a shearing device, in which soft solder or a metallic bonding agent of a synthetic resin group is used for bonding the shearing edge member to the tool body, thus producing a shearing device sufficiently strong in tensile strength and free from strain or formation and adhesion of scales to the tool due to bonding.